1. Field of the Invention
The present invention relates to an ink for ink-jet recording.
2. Description of the Related Art
One of the important characteristics required of an ink for ink-jet recording is that the ink exhibits good ozone resistance. This is to prevent color fading (resulting in a reduction in image quality) of an ink-jet printed material caused by contact with any ozone present in the atmosphere. Meanwhile, a copper phthalocyanine-based dye has been employed as a coloring agent for a cyan ink for ink-jet recording. Such a dye has better light fastness when compared to magenta and yellow dyes but has a problem in that it exhibits insufficient ozone resistance.
Another important characteristic required for an ink for ink-jet recording is that the ink resists the growth of mildew. When mildew grows in an ink, the mildew itself acts as a foreign material. Therefore, the ejection stability of an ink containing mildew from nozzles of an ink-jet head decreases, causing clogging of the nozzles. Hence, a thiazole-based compound is added as a mildew proofing agent to an ink for ink-jet recording, irrespective of whether a copper phthalocyanine dye is employed as a coloring agent or not (U.S. Pat. No. 6,514,330B1).
However, in an ink for ink-jet recording to which a mildew proofing agent composed of a thiazole-based compound is added, although the growth of mildew is suppressed, a further problem exists in that the formation of a precipitate is observed. In particular, this tendency is noted when a copper phthalocyanine dye is employed as a coloring agent. Occasionally, in order to prevent corrosion of metal materials in an ink passage of an ink-jet head, an anticorrosive agent composed of a benzotriazole-based compound is additionally added to the ink. However, a problem exists in this case also in that the formation of a precipitate in the ink is observed.